Electroluminescent Materials and Devices

ABSTRACT

Novel ruthenium, rhodium, palladium, osmium, iridium or platinum complexes of dibenzothiophen ligands are electroluminescent compounds.

The present invention relates to electroluminescent materials and toelectroluminescent devices.

Materials that emit light when an electric current is passed throughthem are well known and used in a wide range of display applications.Devices which are based on inorganic semiconductor systems are widelyused. However these suffer from the disadvantages of high energyconsumption, high cost of manufacture, low quantum efficiency and theinability to make flat panel displays. Organic polymers have beenproposed as useful in electroluminescent devices, but it is not possibleto obtain pure colours; they are expensive to make and have a relativelylow efficiency. Another electroluminescent compound which has beenproposed is aluminium quinolate, but it requires dopants to be used toobtain a range of colours and has a relatively low efficiency.

Patent application WO98/58037 describes a range of transition metal andlanthanide complexes which can be used in electroluminescent deviceswhich have improved properties and give better results. PatentApplications PCT/GB98/01773, PCT/GB99/03619, PCT/GB99/04030,PCT/GB99/04024, PCT/GB99/04028 and PCT/GB00/00268 describeelectroluminescent complexes, structures and devices using rare earthchelates. U.S. Pat. No. 5,128,587 discloses an electroluminescent devicewhich consists of an organometallic complex of rare earth elements ofthe lanthanide series sandwiched between a transparent electrode of highwork function and a second electrode of low work function, with a holeconducting layer interposed between the electroluminescent layer and thetransparent high work function electrode, and an electron conductinglayer interposed between the electroluminescent layer and the electroninjecting low work function anode. The hole conducting layer and theelectron conducting layer are required to improve the working and theefficiency of the device. The hole transporting layer serves totransport holes and to block the electrons, thus preventing electronsfrom moving into the electrode without recombining with holes. Therecombination of carriers therefore mainly takes place in the emitterlayer.

We have now discovered further electroluminescent organometalliccomplexes.

According to the invention there is provided complexes of formula:

-   M is ruthenium, rhodium, palladium, osmium, iridium or platinum;-   n is 1 or 2;-   R¹-R⁵ which may be the same or different are selected from    substituted and unsubstituted hydrocarbyl groups; substituted and    unsubstituted monocyclic and polycyclic heterocyclic groups;    substituted and unsubstituted hydrocarbyloxy or carboxy groups;    fluorocarbyl groups; halogen; nitrile; nitro; amino; alkylamino;    dialkylamino; arylamino; diarylamino; N-alkylamido, N-arylamido,    sulfonyl and thiophenyl; and R² and R³ can additionally be    alkylsilyl or arylsilyl;

p, s and t independently are 0, 1, 2 or 3;

subject to the proviso that where any of p, s and t is 2 or 3 only oneof them can be other than saturated hydrocarbyl or halogen; and

q and r independently are 0, 1 or 2, subject to the proviso that when qor r is 2, only one of them can be other than saturated hydrocarbyl orhalogen.

Preferred compounds of the above class are those in which M is iridium.The preferred value for n is 1.

In those compounds which are ring-substituted, R¹-R⁵ may be asubstituted or unsubstituted C₁-C₁₂ aliphatic or cycloaliphatic groupand in the case of a cycloaliphatic group are preferably based oncyclopentyl or cyclohexyl. Where R¹-R⁵ are heterocyclic, they willnormally be mono- or bicyclic based on 5- or 6-membered rings, forexample furanyl, thiophenyl, pyrrolyl, imidazolyl, pyrazolyl, pyradinyl,pyrimidinyl, pyrazinyl, indolyl or carbazolyl (tricyclic) which may befurther substituted e.g. by methyl or other C₂-C₄ alkyl, methoxy orother C₂-C₄ alkoxy or halogen. As fluorocarbonyl there may be mentionedtrifluoromethyl, and as halogen there may be mentioned fluorine,chlorine or bromine. Substituted amino groups include methylamino,dimethylamino, benzylamino and dibenzylamino. In further possibilities,at least one of R¹-R⁵ may be a substituted or unsubstituted monocyclicor polycyclic aromatic or aryloxy structure. For example, at least oneof R¹-R⁵ may be phenyl, tolyl, fluorophenyl, biphenyl, naphthyl,fluorenyl, anthracenyl or phenanthrenyl.

Readily available compounds of formula (I) include those where R¹-R⁵ areselected from methyl, ethyl, methoxy, ethoxy, fluoro, chloro or bromo.

A particular compound of formula (I) above is that in which M is Ir, nis 1 and p, q, r, s and t are 0.

According to a further aspect of the invention, there is also provided aprocess for manufacturing a compound of formula (I) as defined above.

Synthesis of a dibenzothiophene may be achieved in two steps.α-Haloketones can be prepared by reacting the ketone with chlorine, forexample with cyclohexanone in Organic Synthesis, CV3, 188. Treating athiophenol with an α-halocyclohexanone in the presence of a base e.g.potassium hydroxide, to form a (phenylthio)cyclohexanone as described inU.S. Pat. No. 4,334,078 and a review ‘The Chemistry of α-Haloketones andtheir utility in Hetereocyclic Synthesis’, by A. W. Erian, S. M. Sherifand H. M. Gaber in Molecules, 2003, 8, 793-865.

Treatment of a (phenylthio)cyclohexanone with a cyclodehydrating agent,e.g. polyphosphoric acid, yields the corresponding dibenzothiophene.

An aryl boronic acid derivative of the above dibenzothiophene may beprepared by treating the dibenzothiophene with an organolithium, forexample n-butyllithium, or a Grignard reagent and trialkyl borate, forexample trimethyl borate. Greater regiospecificity may be achieved bysynthesizing a dibenzothiophene in which there is halogen at theposition that it is desired to boronate.

Synthesis of a pyridine-substituted dibenzothiophene ligand may beachieved by a Suzuki coupling reaction of a 2-bromopyridine with a3-dibenzothiopheneboronic acid using a palladium (0) catalyst, forexample tetrakis(triphenylphosphine) palladium e.g. according to thescheme shown below.

Heating a pyridine-substituted dibenzothiophene ligand with iridiumtrichloride gives the following complex:

Further treatment of the above complex with a strong base and additionof (2-pyridyl)benzimidazole or a substituted derivative thereof producesthe compound of formula (I), the substituents having the same meaningsas for formula (I).

In the first step, instead of thiophenol there may be used, for example,2-bromothiophenol, 3-bromothiophenol, 4-bromothiophenol,2-chlorothiophenol, 3-chlorothiophenol, 4-chlorothiophenol,2-fluorothiophenol, 3-fluorothiophenol, 4-fluorothiophenol,2-toluenethiol, 4-toluenethiol, 2-ethylthiophenol, 2-hydroxythiophenol,3-hydroxythiophenol, 4-hydroxythiophenol, 2-methoxythiophenol,3-methoxythiophenol, 4-methoxythiophenol, 3-ethoxythiophenol,2-aminothiophenol, 3-aminothiophenol, 4-aminothiophenol,4-acetamidothiophenol, 4-nitrothiophenol, 3,4-difluorothiophenol,2,4-dimethylthiophenol, 2,5-dimethylthiophenol, 3,4-dimethylthiophenol,3,5-dimethylthiophenol, 2,5-dimethoxythiophenol,3,5-bis(trifluoromethyl)thiophenol,2-nitro-4-(trifluoromethyl)thiophenol or 2-naphthalenethiol. Instead ofcyclohexanone there may be used, for example, 2-methylcyclohexanone,3-methylcyclohexanone, 4-methylcyclohexanone, 4-ethylcyclohexanone,3-isopropylcyclohexanone, 3-(trifluoromethyl)cyclohexanone,2-nitrocyclohexanone or 4-(trimethylsilyl)cyclohexanone.

In the preparation of the pyridine-substituted dibenzothiophene ligandinstead of 2-bromopyridine there may be used, for example,2-iodopyridine, 2-chloropyridine, 2-chloro-5-iodopyridine,2-bromo-5-iodopyridine, 2-amino-5-iodopyridine or2-chloro-5-pyridinecarbonitrile.

The invention also provides an electroluminescent device which comprises(i) a first electrode, (ii) a layer of an electroluminescent material offormula (I) above and (iii) a second electrode.

The thickness of the layer of the electroluminescent material ispreferably from 10-250 nm, more preferably 20-75 nm.

The first electrode can function as the anode and the second electrodecan function as the cathode and preferably there is a layer of a holetransporting material between the anode and the layer of theelectroluminescent compound.

The hole transporting material can be any of the hole transportingmaterials used in electroluminescent devices.

The hole transporting material can be an amine complex such as α-NBP,poly (vinylcarbazole),N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD),an unsubstituted or substituted polymer of an amino substituted aromaticcompound, a polyaniline, substituted polyanilines, polythiophenes,substituted polythiophenes, polysilanes and substituted polysilanes etc.Examples of polyanilines are polymers of:

where R is in the ortho- or meta-position and is hydrogen, C1-18 alkyl,C1-6 alkoxy, amino, chloro, bromo, hydroxy or the group:

where R is alkyl or aryl and R′ is hydrogen, C1-6 alkyl or aryl with atleast one other monomer of formula II above.

Alternatively the hole transporting material can be a polyaniline.Polyanilines which can be used in the present invention have the generalformula:

where p is from 1 to 10 and n is from 1 to 20, R is as defined above andX is an anion, preferably selected from Cl, Br, SO₄, BF₄, PF₆, H₂PO₃,H₂PO₄, arylsulphonate, arenedicarboxylate, polystyrenesulphonate,polyacrylate alkylsulphonate, vinylsulphonate, vinylbenzene sulphonate,cellulose sulphonate, camphor sulphonate, cellulose sulphate or aperfluorinated polyanion.

Examples of arylsulphonates are p-toluenesulphonate, benzenesulphonate,9,10-anthraquinone-sulphonate and anthracenesulphonate. An example of anarenedicarboxylate is phthalate and an example of arenecarboxylate isbenzoate.

We have found that protonated polymers of the unsubstituted orsubstituted polymer of an amino substituted aromatic compound such as apolyaniline are difficult to evaporate or cannot be evaporated. Howeverwe have surprisingly found that if the unsubstituted or substitutedpolymer of an amino substituted aromatic compound is deprotonated, thenit can be easily evaporated, i.e. the polymer is evaporable.

Preferably evaporable deprotonated polymers of unsubstituted orsubstituted polymers of an amino substituted aromatic compound are used.The deprotonated unsubstituted or substituted polymer of an aminosubstituted aromatic compound can be formed by deprotonating the polymerby treatment with an alkali such as ammonium hydroxide or an alkalimetal hydroxide such as sodium hydroxide or potassium hydroxide.

The degree of protonation can be controlled by forming a protonatedpolyaniline and deprotonating. Methods of preparing polyanilines aredescribed in the article by A. G. MacDiarmid and A. F. Epstein, FaradayDiscussions, Chem Soc.88 P319, 1989.

The conductivity of the polyaniline is dependent on the degree ofprotonation with the maximum conductivity being when the degree ofprotonation is between 40 and 60%, for example about 50%.

Preferably the polymer is substantially fully deprotonated.

A polyaniline can be formed of octamer units. i.e. p is four, e.g.

The polyanilines can have conductivities of the order of 1×10⁻¹ Siemencm⁻¹ or higher.

The aromatic rings can be unsubstituted or substituted, e.g. by a C1 to20 alkyl group such as ethyl.

The polyaniline can be a copolymer of aniline and preferred copolymersare the copolymers of aniline with o-anisidine, m-sulphanilic acid oro-aminophenol, or o-toluidine with o-aminophenol, o-ethylaniline,o-phenylene diamine or with amino anthracenes.

Other polymers of an amino substituted aromatic compound which can beused include substituted or unsubstituted polyaminonapthalenes,polyaminoanthracenes, polyaminophenanthrenes, etc. and polymers of anyother condensed polyaromatic compound. Polyaminoanthracenes and methodsof making them are disclosed in U.S. Pat. No. 6,153,726. The aromaticrings can be unsubstituted or substituted, e.g. by a group R as definedabove.

Other hole transporting materials are conjugated polymers and theconjugated polymers which can be used can be any of the conjugatedpolymers disclosed or referred to in U.S. Pat. No. 5,807,627, WO90/13148and WO92/03490.

The preferred conjugated polymers are poly (p-phenylenevinylene) (PPV)and copolymers including PPV. Other preferred polymers arepoly(2,5dialkoxyphenylene vinylene) such aspoly[2-methoxy-5-(2-methoxypentyloxy-1,4-phenylene vinylene)],poly[(2-methoxypentyloxy)-1,4-phenylenevinylene],poly[(2-methoxy-5-(2-dodecyloxy-1,4-phenylenevinylene)] and otherpoly(2,5 dialkoxyphenylenevinylenes) with at least one of the alkoxygroups being a long chain solubilising alkoxy group, polyfluorenes andoligofluorenes, polyphenylenes and oligophenylenes, polyanthracenes andoligoanthracenes, polythiophenes and oligothiophenes.

In PPV the phenylene ring may optionally carry one or more substituents,e.g. each independently selected from alkyl, preferably methyl, oralkoxy, preferably methoxy or ethoxy.

In polyfluorene, the fluorene ring may optionally carry one or moresubstituents e.g. each independently selected from alkyl, preferablymethyl, alkoxy, preferably methoxy or ethoxy.

Any poly(arylenevinylene) including substituted derivatives thereof canbe used and the phenylene ring in poly(p-phenylenevinylene) may bereplaced by a fused ring system such as an anthracene or naphthalenering and the number of vinylene groups in each poly(phenylenevinylene)moiety can be increased, e.g. up to 7 or higher.

The conjugated polymers can be made by the methods disclosed in U.S.Pat. No. 5,807,627, WO90/13148 and WO92/03490.

The thickness of the hole transporting layer is preferably 20 nm to 200nm.

The polymers of an amino substituted aromatic compound such aspolyanilines referred to above can also be used as buffer layers with orin conjunction with other hole transporting materials e.g. between theanode and the hole transporting layer. Other buffer layers can be formedof phthalocyanines such as copper phthalocyanine.

The structural formulae of some other hole transporting materials areshown in FIGS. 3, 4, 5, 6 and 7 of the drawings, where R, R¹, R², R³ andR⁴ can be the same or different and are selected from hydrogen,substituted and unsubstituted hydrocarbyl groups such as substituted andunsubstituted aliphatic groups, substituted and unsubstituted aromatic,heterocyclic and polycyclic ring structures, fluorocarbon groups such astrifluoromethyl, halogens such as fluorine or thiophenyl groups; R, R¹,R², R³ and R⁴ can also form substituted and unsubstituted fusedaromatic, heterocyclic and polycyclic ring structures and can becopolymerisable with a monomer, e.g. styrene. X is Se, S or O, Y can behydrogen, substituted or unsubstituted hydrocarboxyl groups, such assubstituted and unsubstituted aromatic, heterocyclic and polycyclic ringstructures, fluorocarbon groups such as trifluoromethyl, halogens suchas fluorine, thiophenyl or nitrile groups.

Examples of R and/or R¹ and/or R² and/or R³ and/or R⁴ include aliphatic,aromatic and heterocyclic groups, alkoxy, aryloxy and carboxy groups,substituted and unsubstituted phenyl, fluorophenyl, biphenyl, naphthyl,fluorenyl, anthracenyl and phenanthrenyl groups, alkyl groups such ast-butyl, and heterocyclic groups such as carbazole.

Optionally there is a layer of an electron injecting material betweenthe anode and the electroluminescent material layer. The electroninjecting material is a material which will transport electrons when anelectric current is passed through. Electron injecting materials includea metal complex such as a metal quinolate, e.g. an aluminium quinolate,lithium quinolate, zirconium quinolate (Zrq₄), a cyanoanthracene such as9,10-dicyanoanthracene, cyano substituted aromatic compounds,tetracyanoquinodimethane, a polystyrene sulphonate or a compound withthe structural formulae shown in FIGS. 1 or 2 of the drawings orMx(DBM)_(n) where Mx is a metal and DBM is dibenzoyl methane and n isthe valency of Mx e.g. Mx is aluminium or chromium. A Schiff base canalso be used in place of the DBM moiety.

Instead of being a separate layer the electron injecting material can bemixed with the electroluminescent material and co-deposited with it.

Optionally the hole transporting material can be mixed with theelectroluminescent material and co-deposited with it and the electroninjecting materials and the electroluminescent materials can be mixed.The hole transporting materials, the electroluminescent materials andthe electron injecting materials can be mixed together to form onelayer, which simplifies the construction.

The first electrode is preferably a transparent substrate such as aconductive glass or plastic material which acts as the anode; preferredsubstrates are conductive glasses such as indium tin oxide coated glass,but any glass which is conductive or has a conductive layer such as ametal or conductive polymer can be used. Conductive polymers andconductive polymer coated glass or plastics materials can also be usedas the substrate.

The cathode is preferably a low work function metal, e.g. aluminium,barium, calcium, lithium, rare earth metals, transition metals,magnesium and alloys thereof such as silver/magnesium alloys, rare earthmetal alloys etc; aluminium is a preferred metal. A metal fluoride suchas an alkali metal e.g. lithium fluoride or rare earth metal or theiralloys can be used as the second electrode, for example by having ametal fluoride layer formed on a metal.

The iridium or other metal complex can be mixed with a host material

The devices of the present invention can be used as displays in videodisplays, mobile telephones, portable computers and any otherapplication where an electronically controlled visual image is used. Thedevices of the present invention can be used in both active and passiveapplications of such as displays.

In known electroluminescent devices either one or both electrodes can beformed of silicon and the electroluminescent material and interveninglayers of hole transporting and electron transporting materials can beformed as pixels on the silicon substrate. Preferably each pixelcomprises at least one layer of an electroluminescent material and a (atleast semi-) transparent electrode in contact with the organic layer ona side thereof remote from the substrate.

Preferably, the substrate is of crystalline silicon and the surface ofthe substrate may be polished or smoothed to produce a flat surfaceprior to the deposition of electrode, or electroluminescent compound.Alternatively a non-planarised silicon substrate can be coated with alayer of conducting polymer to provide a smooth, flat surface prior todeposition of further materials.

In one embodiment, each pixel comprises a metal electrode in contactwith the substrate. Depending on the relative work functions of themetal and transparent electrodes, either may serve as the anode with theother constituting the cathode.

When the silicon substrate is the cathode an indium tin oxide coatedglass can act as the anode and light is emitted through the anode. Whenthe silicon substrate acts as the anode, the cathode can be formed of atransparent electrode which has a suitable work function; for example byan indium zinc oxide coated glass in which the indium zinc oxide has alow work function. The anode can have a transparent coating of a metalformed on it to give a suitable work function. These devices aresometimes referred to as top emitting devices or back emitting devices.

The metal electrode may consist of a plurality of metal layers; forexample a higher work function metal such as aluminium deposited on thesubstrate and a lower work function metal such as calcium deposited onthe higher work function metal. In another example, a further layer ofconducting polymer lies on top of a stable metal such as aluminium.

Preferably, the electrode also acts as a mirror behind each pixel and iseither deposited on, or sunk into, the planarised surface of thesubstrate. However, there may alternatively be a light absorbing blacklayer adjacent to the substrate.

In still another embodiment, selective regions of a bottom conductingpolymer layer are made non-conducting by exposure to a suitable aqueoussolution allowing formation of arrays of conducting pixel pads whichserve as the bottom contacts of the pixel electrodes.

1. An electroluminescent compound of formula:

M is ruthenium, rhodium, palladium, osmium, iridium or platinum; n is 1or 2; R₁ to R₅ which may be the same or different are selected fromsubstituted and unsubstituted hydrocarbyl groups; substituted andunsubstituted monocyclic and polycyclic heterocyclic groups; substitutedand unsubstituted hydrocarbyloxy or carboxy groups; fluorocarbyl groups;halogen; nitrile; nitro; amino; alkylamino; dialkylamino; arylamino;diarylamino; N-alkylamido, N-arylamido, sulfonyl and thiophenyl; and R²and R³ can additionally be alkylsilyl or arylsilyl; p, s and tindependently are 0, 1, 2 or 3; q and r independently are 0, 1 or 2,subject to the provisos that: where p is 2, one of the R₁ groups isselected from saturated hydrocarbyl and halogen and the other is asdefined above; where p is 3, two of the R₁ groups are selected fromsaturated hydrocarbyl and halogen and the other is as defined above;where q is 2, one of the R2 groups is selected from saturatedhydrocarbyl and halogen and the other is as defined above; where r is 2,one of the R₃ groups is selected from saturated hydrocarbyl and halogenand the other is as defined above; where s is 2, one of the R₄ groups isselected from saturated hydrocarbyl and halogen and the other is asdefined above; where s is 3, two of the R₄ groups are selected fromsaturated hydrocarbyl and halogen and the other is as defined above;where t is 2, one of the R₅ groups is selected from saturatedhydrocarbyl and halogen and the other is as defined above; and where tis 3, two of the R₅ groups are selected from saturated hydrocarbyl andhalogen and the other is as defined above.
 2. The compound of claim 1,wherein M is iridium.
 3. The compound of claim 1, wherein n is
 1. 4. Thecompound of claim 1, wherein at least one of R₁ to R₅ is a substitutedor unsubstituted aliphatic or cycloaliphatic group.
 5. The compound ofclaim 4, wherein least one of R₁ to R₅ is alkyl or alkoxy.
 6. Thecompound of claim 5, wherein at least one of R₁ to R₅ is methyl, ethyl,n-propyl, i-propyl. s-butyl, t-butyl, cyclohexyl, methoxy or ethoxy. 7.The compound of claim 1, wherein at least one of R₁ to R₅ is asubstituted or unsubstituted monocyclic or polycyclic aromatic, aryloxyor heterocyclic group.
 8. The compound of claim 7, wherein at least oneof R₁ to R₅ is phenyl, tolyl, fluorophenyl, biphenyl, naphthyl,fluorenyl, anthracenyl, phenanthrenyl or carbazolyl.
 9. The compound ofclaim 1, wherein at least one of R₁ to R₅ is fluoro, chloro,methylamino, dimethylamino, benzylamino or dibenzylamino.
 10. Thecompound of claim 1, wherein at least one of R₂ and R₃ is trialkylsilylor triarylsilyl.
 11. The compound of claim 1, wherein M is Ir, n is 1and p, q, r, s and t are
 0. 12. An electroluminescent device comprising(i) a first electrode, (ii) a second electrode and (iii) of anelectroluminescent layer comprising an electroluminescent compoundaccording to claim 1 located between the first electrode and the secondelectrode.
 13. The device of claim 12, wherein a layer of a holetransmitting material is located between the first electrode and theelectroluminescent layer.
 14. The device of claim 13, in which the holetransmitting material is an aromatic amine complex.
 15. The device ofclaim 13, in which the hole transmitting material is a polyaromaticamine complex.
 16. The device of claim 13, in which the holetransmitting material is a film of a material selected from α-NBP,poly(vinylcarbazole),N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD),polyaniline, substituted polyanilines, polythiophenes, substitutedpolythiophenes, polysilanes and substituted polysilanes.
 17. The deviceof claim 13, in which the hole transmitting material is a film of acompound which is (a) a polymer of at least two monomers of formula

where R is in the ortho- or meta-position and is selected from hydrogen,C₁ to C₁₈ alkyl, C₁ to C₆ alkoxy, amino, chloro, bromo, hydroxy or thegroup:

where R is alkyl or aryl and R′ is selected from hydrogen, C₁ to C₆alkyl or aryl; or which is (b) a polyaniline of formula:

where p is from 1 to 10 and n is from 1 to 20, R is as defined above andX is an anion or which is (c) a compound selected from FIGS. 3 to 7 ofthe drawings.
 18. The device of claim 13, in which the hole transmittingmaterial is a copolymer of aniline, a copolymer of aniline witho-anisidine, m-sulphanilic acid or o-aminophenol, or o-toluidine witho-aminophenol, o-ethylaniline, o-phenylene diamine or with an aminoanthracene.
 19. The device of claim 13, in which the hole transmittingmaterial is a conjugated polymer.
 20. The device of claim 19, in whichthe conjugated polymer is selected from poly (p-phenylenevinylene) (PPV)and copolymers including PPV, poly(2,5dialkoxyphenylene vinylene),poly(2-methoxy-5-(2-methoxypentyloxy-1,4-phenylene vinylene),poly(2-methoxypentyloxy)-1,4-phenylenevinylene),poly(2-methoxy-5-(2-dodecyloxy-1,4-phenylenevinylene) and otherpoly(2,5dialkoxyphenylenevinylenes) with at least one of the alkoxygroups being a long chain solubilising alkoxy group, polyfluorenes andoligofluorenes, polyphenylenes and oligophenylenes, polyanthracenes andoligo anthracenes, polythiophenes and oligothiophenes.
 21. The device ofclaim 12 in which the electroluminescent layer comprises anelectroluminescent compound in admixture with a hole transmittingmaterial.
 22. The device of claim 12, wherein a layer of an electrontransmitting material is located between an electrode that serves as acathode and the electroluminescent layer.
 23. The device of claim 22 inwhich the electron transmitting material is a metal quinolate.
 24. Thedevice of claim 23, in which the metal quinolate is an aluminumquinolate, zirconium quinolate or lithium quinolate.
 25. The device ofclaim 22, in which the electron transmitting material is of formulaMx(DBM)_(n) where Mx is a metal and DBM is dibenzoyl methane and n isthe valency of Mx.
 26. The device of claim 25, in which the electrontransmitting material is a cyanoanthracene, a polystyrene sulphonate ora compound of formulae shown in FIG. 1 or 2 of the drawings.
 27. Thedevice of claim 12, in which an electron transmitting material is inadmixture with the electroluminescent compound.
 28. The device of claim12, in which the first electrode is a transparent electricallyconducting glass electrode.
 29. The device of claim 12, in which thesecond electrode is selected from aluminum, barium, rare earth metals,transition metals, calcium, lithium, magnesium and alloys thereof andsilver/magnesium alloys.
 30. The device of claim 12, wherein the secondelectrode comprises a metal having a metal fluoride layer formed on it.31. The device of claim 30, wherein the metal fluoride is a lithiumfluoride or rare earth fluoride.
 32. The compound of claim 1, wherein p,q, r, s and t independently are 0 or
 1. 33. An electroluminescent devicecomprising (i) a first electrode, (ii) a second electrode, and (iii) anelectroluminescent layer comprising a compound according to claim 32located between the first electrode and the second electrode.